The present invention relates to a method for diagnosing the mixture formation in internal combustion engines including tank ventilation.
It is conventional to superpose a precontrol with a closed-loop control in controlling the air-fuel ratio for internal combustion engines. Furthermore, it is conventional to derive further correcting quantities from the behavior of the controlled variable to compensate for incorrect adaptations of the precontrol in response to changed operating conditions. This compensation is also referred to as adaptation. U.S. Pat. No. 4,584,982, for instance, describes an adaptation using different adaptation quantities in different ranges of the load/rotational speed spectrum of an internal combustion engine. The different adaptation quantities relate to the compensation of different faults. Based on cause and effect, a distinction may be made between three kinds of faults: faults in a hot-film air-mass meter have a multiplicative effect on the fuel metering. Leakage-air impacts have an additive effect per time unit, and faults in the compensation of the pickup time of the injectors have an additive effect per injection.
In accordance with mandatory regulations, emission-relevant faults are to be detected by an on-board arrangement and a fault light is activated, if appropriate. The mixture adaptation is also used in fault diagnosis. For instance, a fault is indicated if the corrective adjustment of the adaptation is excessive.
The diagnosis of the fuel-supply system is linked to the mixture adaptation, which may only run during active lambda control, that is, especially not in operating modes in which lambda is merely controlled (for example, in stratified operation with direct fuel injection (BDE), in uncontrolled lean-combustion operation with BDE and in intake-manifold injection).
Thus, for the adaptation, a switch to homogenous operation occurs and the mixture adaptation is activated.
An engine control program is referred to in German Published Patent Application No. 1 98 50 586, which controls the switchover between stratified operation and homogeneous operation.
In stratified operation, the engine is operated with a heavily stratified cylinder charge and a high excess of air, so as to keep the fuel consumption as low as possible. The stratified charge is obtained by retarded fuel injection, which ideally leads to a division of the combustion chamber into two zones: The first zone contains the combustible air-fuel mixture at the spark plug. It is surrounded by the second zone, consisting of an insulating layer of air and residual gas. The potential for optimizing fuel consumption results from the possibility of operating the engine mostly without throttle control while avoiding charge-cycle losses. With comparatively low charge, stratified operation may be preferred.
With higher charge, when the primary goal is to optimize performance, the engine is operated with homogeneous cylinder charge. The homogeneous cylinder charge results from early fuel injection during the intake step. In this manner, there is more time available to form the mixture before combustion occurs. The potential for optimizing performance offered by this operating mode results, for instance, from utilizing the entire combustion-chamber volume for the filling with combustible mixture.
Several activation conditions exist for adaptation:
For instance, the engine temperature has reached the activation-temperature threshold, and the lambda probe is operative. Furthermore, the instantaneous values of charge and speed are each within certain ranges in which learning occurs. This is referred to in U.S. Pat. No. 4,584,982, for instance. Also, homogeneous operation is given.
The present invention seeks to expand the time period during which the engine may be operated in stratified operation at optimum fuel consumption. The switch-over to homogeneous operation for diagnostic purposes reduces the fuel-consumption advantage of direct fuel injection, since homogeneous operation is less economical than stratified operation. Therefore, switching to homogeneous operation causes an unnecessary increase in fuel consumption in those cases where no fault is present. It should be avoided whenever possible, without decreasing the chance of detecting faults related to exhaust gas.
This desired effect is achieved by a method for diagnosing the mixture formation in internal combustion engines including combustion chambers and tank ventilation. In this context, the diagnosis is linked to mixture adaptation, which only runs during active lambda control and in which, outside of active lambda control, an indication of a mixture or probe fault is detected by generation of a fault suspicion during active tank ventilation and non-active mixture adaptation in those cases where a measurement for the influence of the tank ventilation on the mixture composition, which is formed assuming an intact system, takes on implausible values. When this is suspected, the mixture adaptation is requested, so that the assumption may either be verified or falsified.
In a further refinement of the present invention, the internal combustion engine is operated with direct fuel injection into the combustion chambers.
A further refinement distinguishes itself by the internal combustion engine being operated, in at least one first operating mode, using stratified mixture distribution in the combustion chambers (stratified operation) and, in a second operating mode, using homogeneous mixture distribution in the combustion chambers (homogeneous operation) and an indication of a mixture or probe fault (fault suspicion) is detected outside of active lambda control, in stratified operation.
A further measure provides that a switchover to homogeneous operation occurs for diagnostic purposes when an indication of a mixture or probe fault (fault suspicion) is detected in stratified operation, so that the fault suspicion may be verified or falsified.
A further measure provides for the use of a control device to control a tank ventilation system 12 and further functions in order to achieve efficient combustion of the fuel/air mixture in the combustion chamber, the tank ventilation system 12 including an activated carbon-filter 18, which is connected via appropriate lines or connections to the tank, the ambient air, and to the intake manifold of the internal combustion engine, and which also includes a tank ventilation valve 16 arranged in the line to the intake manifold.
According to another further refinement, a precontrol value rk for a fuel-metering signal for fuel injection into at least one of the combustion chambers is formed as a function of at least speed n, and a signal ml is generated regarding the air quantity drawn in by the internal combustion engine. A faulty adaptation of the fuel quantity to the air quantity is reflected in signal Us of an exhaust-gas analyzer probe, from which a controller 2.3 forms a controlled variable fr, which reduces the faulty adaptation by a multiplicative linking with precontrol value rk.
A further measure provides for the formation of an adaptation operation fra of the fuel-metering signal formation, by forming an average value frm of control variable fr, and by correcting the fuel-metering signal formation by an adaptation-operation variable fra, which is based on the mentioned average value.
An additional measure provides that tank ventilation but no mixture adaptation occurs in stratified operation.
According to a further refinement, the influence of the regeneration gas on the composition of the total fuel/air ratio given active tank ventilation is derived from the signal of a lambda probe, from which the fuel concentration (=charge) of the regeneration gas is learned (adapted), and the fuel portion introduced via the Tank Ventilation Valve(TEV) calculated using the following input variables:
signal of exhaust-gas analyzer probe;
measured intake air quantity;
fuel quantity metered via injectors;
regeneration-gas quantity, derivable from the control pulse-duty factor for the tank-ventilation valve and further boundary conditions.
A further refinement provides that a fault is set in those cases where the charge of the regeneration gas of the Tank Ventilation (TV) is outside a plausible range.
The present invention also relates to an electronic control device for implementing the methods in accordance with the aforementioned methods and further refinements for diagnosing a mixture formation.
Therefore, the present invention represents a method for diagnosing the mixture formation in internal combustion engines including tank ventilation, the diagnosis is linked to the mixture adaptation and is only able to execute given active lambda control. Therefore, the mixture adaptation especially does not run in operating modes of the internal combustion engine in which lambda is merely controlled. The method distinguishes itself by the fact that, outside of active lambda control, an indication of a mixture or probe fault is also recognized in stratified, or lean operation, e.g., in DFI, but basically also in lean operation in manifold injection. For that purpose, a fault suspicion is set with active tank ventilation and non-active mixture adaptation. If, in this context, a measurement for the influence of the tank ventilation on the mixture composition, which is formed assuming an intact system, takes on implausible values, the mixture adaptation is requested in order to possibly verify the suspicion.
Indicating a suspected fault for the mixture during tank ventilation may be advantageous in case of DFI-engines, since faults may be detected not only in stratified but also in homogenous operation, and activation of the mixture adaptation is thus possible. The mixture adaptation itself requires active lambda control, i.e., homogeneous operation, and, may thus not be activated and is unable to detect faults in stratified operation. A switchover to homogenous operation merely for diagnostic purposes occurs only if a reason exists for suspecting a fault, in this manner preventing an undesired limitation of stratified operation.